U.S. patent application number 13/272818 was filed with the patent office on 2012-04-19 for determination of electromagnetic properties of samples.
This patent application is currently assigned to Katholieke Universiteit Leuven, K.U. Leuven R&D. Invention is credited to Steven Brebels, Walter De Raedt, Amin Enayati, Guy Vandenbosch.
Application Number | 20120092674 13/272818 |
Document ID | / |
Family ID | 44936173 |
Filed Date | 2012-04-19 |
United States Patent
Application |
20120092674 |
Kind Code |
A1 |
Enayati; Amin ; et
al. |
April 19, 2012 |
Determination of Electromagnetic Properties of Samples
Abstract
Disclosed are methods and devices for measuring electromagnetic
properties of samples. In one embodiment, a device is disclosed
that includes a substantially two-dimensional measurement chamber
comprising a reflective surface, where the reflective surface has a
substantially elliptical shape that forms a part of an ellipse
having a first focal point and a second focal point. The device
further includes an input/output port located at the first focal
point and a sample holder located at the second focal point.
Inventors: |
Enayati; Amin; (Leuven,
BE) ; Brebels; Steven; (Hechtel-Eksel, BE) ;
De Raedt; Walter; (Lint, BE) ; Vandenbosch; Guy;
(Heindonk (Willebroek), BE) |
Assignee: |
Katholieke Universiteit Leuven,
K.U. Leuven R&D
Leuven
BE
IMEC
Leuven
BE
|
Family ID: |
44936173 |
Appl. No.: |
13/272818 |
Filed: |
October 13, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61392725 |
Oct 13, 2010 |
|
|
|
Current U.S.
Class: |
356/445 ;
356/244 |
Current CPC
Class: |
G01N 22/00 20130101 |
Class at
Publication: |
356/445 ;
356/244 |
International
Class: |
G01N 21/55 20060101
G01N021/55; G01N 21/01 20060101 G01N021/01 |
Claims
1. A measurement device comprising: a substantially two-dimensional
measurement chamber comprising: a reflective surface, wherein the
reflective surface has a substantially elliptical shape that forms
a part of an ellipse having a first focal point and a second focal
point; an input/output port located at the first focal point; and a
sample holder located at the second focal point.
2. The measurement device of claim 1, wherein: the sample holder is
configured to hold a sample; the input/output port is configured to
transmit an electromagnetic signal towards the reflective surface;
the reflective surface is configured to reflect the electromagnetic
signal towards the sample; the sample is configured to reflect a
reflection of the electromagnetic signal towards the reflective
surface; and the reflective surface is configured to reflect the
reflection of the electromagnetic signal towards the input/output
port.
3. The measurement device of claim 2, further comprising a
processor coupled to the input/output port and configured to
process the reflection of the electromagnetic signal to measure at
least one electromagnetic property.
4. The measurement device of claim 3, wherein the processor is
coupled to the input/output port via one of a coaxial cable and a
waveguide.
5. The measurement device of claim 1, wherein walls of the
measurement chamber comprise a material configured to absorb the
electromagnetic signal.
6. The measurement device of claim 1, wherein the input/output port
comprises at least one of a probe, a waveguide, a loop, an
aperture, and an antenna.
7. The measurement device of claim 1, wherein the measurement
chamber being substantially two-dimensional comprises: the
electromagnetic signal having a wavelength; and the measurement
chamber having a thickness on the order of the wavelength.
8. A measurement device comprising: a substantially two-dimensional
measurement chamber comprising: a first reflective surface, wherein
the first reflective surface has a substantially elliptical shape
that forms a part of a first ellipse having a first focal point and
a second focal point; a second reflective surface, wherein the
second reflective surface has a substantially elliptical shape that
forms a part of a second ellipse having a third focal point and a
fourth focal point, wherein the fourth focal point is coincident
with the second focal point; a first input/output port located at
the first focal point; a second input/output port located at the
third focal point; and a sample holder located at the second and
fourth focal points.
9. The measurement device of claim 8, wherein: the sample holder is
configured to hold a sample; the first input/output port is
configured to transmit an electromagnetic signal towards the first
reflective surface; the first reflective surface is configured to
reflect the electromagnetic signal towards the sample; the sample
is configured to (i) transmit a transmission of the electromagnetic
signal towards the second reflective surface and (ii) reflect a
reflection of the electromagnetic signal towards the first
reflective surface; the first reflective surface is further
configured to reflect the reflection of the electromagnetic signal
towards the first input/output port; and the second reflective
surface is configured to reflect the transmission of the
electromagnetic signal towards the second input/output port.
10. The measurement device of claim 9, further comprising: a first
processor coupled to the first input/output port and configured to
process the reflection of the electromagnetic signal to measure at
least one electromagnetic property; and a second processor coupled
to the second input/output port and configured to process the
transmission of the electromagnetic signal to measure at least one
electromagnetic property.
11. The measurement device of claim 10, wherein: the first
processor is coupled to the first input/output port via one of a
coaxial cable and a waveguide; and the second processor is coupled
to the second input/output port via one of a coaxial cable and a
waveguide.
12. The measurement device of claim 9, wherein: the electromagnetic
signal comprises a first electromagnetic signal; the second
input/output port is configured to transmit a second
electromagnetic signal towards the second reflective surface; the
second reflective surface is configured to reflect the second
electromagnetic signal towards the sample; the sample is configured
to (i) transmit a transmission of the second electromagnetic signal
towards the first reflective surface and (ii) reflect a reflection
of the second electromagnetic signal towards the second reflective
surface; the second reflective surface is further configured to
reflect the reflection of the second electromagnetic signal towards
the second input/output port; and the first reflective surface is
configured to reflect the transmission of the second
electromagnetic signal towards the first input/output port.
13. The measurement device of claim 12, wherein the first
electromagnetic signal is of a first wavelength and the second
electromagnetic signal is of second wavelength that differs from
the first wavelength.
14. The measurement device of claim 8, wherein walls of the
measurement chamber comprise a material configured to absorb the
electromagnetic signal.
15. The measurement device of claim 8, wherein each of the first
input/output port and the second input/output port comprises at
least one of a probe, a waveguide, a loop, an aperture, and an
antenna.
16. The measurement device of claim 8, wherein the measurement
chamber being substantially two-dimensional comprises: the
electromagnetic signal having a wavelength; and the measurement
chamber having a thickness on the order of the wavelength.
17. A method comprising: providing a sample in a substantially
two-dimensional measurement chamber; transmitting an
electromagnetic signal from an input/output port towards a
reflective surface in the measurement chamber; reflecting the
electromagnetic signal off the reflective surface towards the
sample; reflecting a reflection of the electromagnetic signal off
the sample towards the reflective surface; reflecting the
reflection of the electromagnetic signal off the reflective surface
towards the input/output port; based on the reflection of the
electromagnetic signal, measuring at least one electromagnetic
property of the sample.
18. The method of claim 17, wherein the reflective surface
comprises a first reflective surface and the input/output port
comprises a first input/output port, the method further comprising:
transmitting a transmission of the electromagnetic signal off the
sample towards a second reflective surface in the measurement
chamber; reflecting the transmission of the electromagnetic signal
off the second reflective surface towards a second input/output
port; and based on the transmission of the electromagnetic signal,
measuring at least one electromagnetic property of the sample.
19. The method of claim 18, wherein the electromagnetic signal
comprises a first electromagnetic signal, the method further
comprising: transmitting a second electromagnetic signal from the
second input/output port towards the second reflective surface in
the measurement chamber; reflecting the second electromagnetic
signal off the second reflective surface towards the sample;
reflecting a reflection of the second electromagnetic signal off
the sample towards the second reflective surface; transmitting a
transmission of the second electromagnetic signal off the sample
towards the first reflective surface; reflecting the reflection of
the electromagnetic signal off the second reflective surface
towards the second input/output port; reflecting the transmission
of the electromagnetic signal off the first reflective surface
towards the first input/output port; and based on the reflection
and the transmission of the second electromagnetic signal,
measuring at least one electromagnetic property of the sample.
20. The method of claim 19, wherein the first electromagnetic
signal is of a first wavelength and the second electromagnetic
signal is of second wavelength that differs from the first
wavelength.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a non-provisional of U.S. Provisional
Patent Application Ser. No. 61/392,725 filed Oct. 13, 2010, the
contents of which are hereby incorporated by reference.
BACKGROUND
[0002] There are many ways in which electromagnetic properties of
materials may be tested. Some of these are non-destructive, such
as, for example, the system disclosed in Darling, U.S. Pat. No.
5,574,379. Darling's system allows measurement of the
electromagnetic properties of a component. In Darling's system,
electromagnetic energy (e.g., microwave energy) is directed towards
the component being tested and the reflected energy is analysed to
indicate the resistivity or magnetic susceptibility of the
component.
[0003] Further, there are many ways in which materials may be
characterized at millimeter and sub-millimeter frequencies. For
example, Aguirre, U.S. Pat. No. 4,507,602 describes a system for
measuring the properties of a sample. According to Aguirre, the
sample is positioned between two sectoral horns that are placed
mouth-to-mouth with the sample in between. An input signal in the
Ku band (e.g., 12.4 to 18 GHz) is supplied to the sample via one
horn and the transmitted and reflected signals from the sample are
received at respective horns. The transmitted and reflected signals
are then analysed to determine the complex permittivity and
permeability of the sample.
[0004] Permittivity measurements may also be performed on printed
wiring, circuit boards, thin films and other substrates in order to
measure their integrity. This is described by, for example,
Baker-Jarvis et al. in "Dielectric Measurements on Printed Wiring
and Circuit Boards, Thin Films and Substrates: An Overview", Mat.
Res. Soc. Sympo. Proc., Vol. 381, 1995.
[0005] Another way in which electromagnetic properties may be
measured is through the use of Fabry-Perot resonators. Fabry-Perot
resonators may use microwaves, as described by, for example, R. N.
Clarke et al. in "Fabry-Perot and Open Resonators at Microwave and
Millimetre Wave Frequencies, 2-300 GTHz", J. Phys. E: Sci.
Instrum., Vol. 15, 1982. Properties that can be measured include
dielectric constant, anisotropy, and magnetic resonance.
[0006] The measurement of dielectric constants is also described
by, for example, T. Zwick et al. in "Determination of the Complex
Permittivity of Packaging Materials at Millimeter-Wave
Frequencies", IEEE Trans. Microw. Theory Tech., Vol. 54, no. 3,
2006. Frequencies from below 20 to 100 GHz are used for performing
measurements on thin sheet substrate materials.
[0007] J. Krupka explains in "Frequency Domain Complex Permittivity
Measurements at Microwave Frequencies", Meas. Sci. Technol., Vol.
17, pages 55 to 70, 2006 that corrugated horn antennas can be used
with elliptical surfaces for measuring laminar samples.
[0008] Jean et al., U.S. Pat. No. 5,455,516, describe a method and
apparatus for the measurement of moisture in a material. According
to Jean, microwave energy is coupled to a measurement chamber via a
coaxial transmission line over a multi-octave bandwidth via an
intermediate microstrip-to-slotline coupling circuit.
[0009] However, most of these methods or techniques use samples
with large dimensions and tend to be unsuitable for measuring the
electromagnetic properties of small samples. In addition, the
sample needs to be correctly positioned within a three-dimensional
space so that misalignment aberrations do not have an impact on the
accuracy of the measurement.
[0010] Moreover, known methods and apparatuses tend to be
over-complicated for measuring small samples, particularly
synthesised materials, such as carbon nanotubes and graphene, where
the size of the samples is limited.
SUMMARY
[0011] Disclosed are methods and systems for determining
electromagnetic properties of small samples.
[0012] The disclosed methods and apparatuses may provide a
simplified technique measuring electromagnetic properties of small
samples, as compared with typical techniques.
[0013] The disclosed methods and systems may additionally allow for
the measurement of any material parameter that can be determined
from the electromagnetic properties.
[0014] The disclosed methods and systems may additionally allow for
the measurement of electromagnetic properties at millimeter and
sub-millimeter wave frequencies for samples with dimensions in the
range of a few millimeters by a few millimeters. Smaller samples
are possible as well.
[0015] In one aspect, a measurement device is disclosed. The
measurement device includes a substantially two-dimensional
measurement chamber comprising a reflective surface, where the
reflective surface has a substantially elliptical shape that forms
a part of an ellipse having a first focal point and a second focal
point. The measurement chamber further comprises an input/output
port located at the first focal point and a sample holder located
at the second focal point.
[0016] In some embodiments, the sample holder is configured to hold
a sample, the input/output port is configured to transmit an
electromagnetic signal towards the reflective surface, the
reflective surface is configured to reflect the electromagnetic
signal towards the sample, the sample is configured to reflect a
reflection of the electromagnetic signal towards the reflective
surface, and the reflective surface is configured to reflect the
reflection of the electromagnetic signal towards the input/output
port. In these embodiments, the measurement device may further
include a processor coupled to the input/output port and configured
to process the reflection of the electromagnetic signal to measure
at least one electromagnetic property. The processor may be coupled
to the input/output port via one of a coaxial cable and a
waveguide.
[0017] In some embodiments, walls of the measurement chamber
comprise a material configured to absorb the electromagnetic
signal.
[0018] In some embodiments, the input/output port comprises at
least one of a probe, a waveguide, a loop, an aperture, and an
antenna.
[0019] In some embodiments, the measurement chamber being
substantially two-dimensional comprises the electromagnetic signal
having a wavelength and the measurement chamber having a thickness
on the order of the wavelength.
[0020] In another aspect, a measurement device is disclosed that
comprises a substantially two-dimensional measurement chamber
comprising a first reflective surface, where the first reflective
surface has a substantially elliptical shape that forms a part of a
first ellipse having a first focal point and a second focal point.
The measurement chamber further comprises a second reflective
surface, where the second reflective surface has a substantially
elliptical shape that forms a part of a second ellipse having a
third focal point and a fourth focal point, where the fourth focal
point is coincident with the second focal point. The measurement
chamber further comprises a first input/output port located at the
first focal point, a second input/output port located at the third
focal point, and a sample holder located at the second and fourth
focal points.
[0021] In some embodiments, the sample holder is configured to hold
a sample, the first input/output port is configured to transmit an
electromagnetic signal towards the first reflective surface, the
first reflective surface is configured to reflect the
electromagnetic signal towards the sample, the sample is configured
to (i) transmit a transmission of the electromagnetic signal
towards the second reflective surface and (ii) reflect a reflection
of the electromagnetic signal towards the first reflective surface,
the first reflective surface is further configured to reflect the
reflection of the electromagnetic signal towards the first
input/output port, and the second reflective surface is configured
to reflect the transmission of the electromagnetic signal towards
the second input/output port.
[0022] In some embodiments, the measurement device further
comprises a first processor coupled to the first input/output port
and configured to process the reflection of the electromagnetic
signal to measure at least one electromagnetic property, and a
second processor coupled to the second input/output port and
configured to process the transmission of the electromagnetic
signal to measure at least one electromagnetic property. The first
processor may be coupled to the first input/output port via one of
a coaxial cable and a waveguide, and the second processor is
coupled to the second input/output port via one of a coaxial cable
and a waveguide.
[0023] In some embodiments, the electromagnetic signal comprises a
first electromagnetic signal, the second input/output port is
configured to transmit a second electromagnetic signal towards the
second reflective surface, the second reflective surface is
configured to reflect the second electromagnetic signal towards the
sample, the sample is configured to (i) transmit a transmission of
the second electromagnetic signal towards the first reflective
surface and (ii) reflect a reflection of the second electromagnetic
signal towards the second reflective surface, the second reflective
surface is further configured to reflect the reflection of the
second electromagnetic signal towards the second input/output port,
and the first reflective surface is configured to reflect the
transmission of the second electromagnetic signal towards the first
input/output port. In these embodiments, the first electromagnetic
signal may be of a first wavelength and the second electromagnetic
signal may be of second wavelength that differs from the first
wavelength.
[0024] In some embodiments, walls of the measurement chamber
comprise a material configured to absorb the electromagnetic
signal.
[0025] In some embodiments, each of the first input/output port and
the second input/output port comprises at least one of a probe, a
waveguide, a loop, an aperture, and an antenna.
[0026] In some embodiments, the measurement chamber being
substantially two-dimensional comprises the electromagnetic signal
having a wavelength and the measurement chamber having a thickness
on the order of the wavelength.
[0027] In yet another aspect, a method is disclosed. The method
comprises providing a sample in a substantially two-dimensional
measurement chamber, transmitting an electromagnetic signal from an
input/output port towards a reflective surface in the measurement
chamber, reflecting the electromagnetic signal off the reflective
surface towards the sample, reflecting a reflection of the
electromagnetic signal off the sample towards the reflective
surface, reflecting the reflection of the electromagnetic signal
off the reflective surface towards the input/output port and, based
on the reflection of the electromagnetic signal, measuring at least
one electromagnetic property of the sample.
[0028] In some embodiments, the reflective surface comprises a
first reflective surface and the input/output port comprises a
first input/output port, and the method further comprises
transmitting a transmission of the electromagnetic signal off the
sample towards a second reflective surface in the measurement
chamber, reflecting the transmission of the electromagnetic signal
off the second reflective surface towards a second input/output
port, and, based on the transmission of the electromagnetic signal,
measuring at least one electromagnetic property of the sample.
[0029] Further, in some embodiments the electromagnetic signal
comprises a first electromagnetic signal, and the method further
comprises transmitting a second electromagnetic signal from the
second input/output port towards the second reflective surface in
the measurement chamber, reflecting the second electromagnetic
signal off the second reflective surface towards the sample,
reflecting a reflection of the second electromagnetic signal off
the sample towards the second reflective surface, transmitting a
transmission of the second electromagnetic signal off the sample
towards the first reflective surface, reflecting the reflection of
the electromagnetic signal off the second reflective surface
towards the second input/output port, reflecting the transmission
of the electromagnetic signal off the first reflective surface
towards the first input/output port and, based on the reflection
and the transmission of the second electromagnetic signal,
measuring at least one electromagnetic property of the sample. In
these embodiments, the first electromagnetic signal may be of a
first wavelength and the second electromagnetic signal may be of
second wavelength that differs from the first wavelength.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] For a better understanding of the present invention,
reference will now be made, by way of example only, to the
accompanying drawings in which:
[0031] FIG. 1 is a schematic illustration of an example measurement
device, in accordance with an embodiment;
[0032] FIG. 2 is a schematic illustration of another example
measurement device, in accordance with an embodiment;
[0033] FIG. 3 illustrates a radiation field distribution in the
example measurement device shown in FIG. 2, in accordance with an
embodiment;
[0034] FIG. 4 is a perspective illustration of the example
measurement device shown in
[0035] FIG. 2, in accordance with an embodiment;
[0036] FIG. 5 is a schematic illustration of another example
measurement device, in accordance with an embodiment;
[0037] FIG. 6 illustrates a radiation field distribution in the
example measurement device shown in FIG. 5, in accordance with an
embodiment; and
[0038] FIG. 7 illustrates a graph of insertion and return losses as
a function of frequency for an example measurement device, in
accordance with an embodiment.
DETAILED DESCRIPTION
[0039] The present invention will be described with respect to
particular embodiments and with reference to certain drawings but
the invention is not limited thereto. The drawings described are
only schematic and are non-limiting. In the drawings, the size of
some of the elements may be exaggerated and not drawn on scale for
illustrative purposes.
[0040] It will be understood that the terms "vertical" and
"horizontal" are used herein refer to particular orientations of
the Figures and these terms are not limitations to the specific
embodiments described herein.
[0041] The terms "first", "second", "third" and the like are used
in the description for distinguishing between similar elements and
not necessarily for describing a sequential or chronological order.
It will be appreciated that the terms are interchangeable under
appropriate circumstances and that the embodiments of the invention
can operate in other sequences than described or illustrated herein
if necessary.
[0042] While the following description discusses determining
particular electromagnetic properties (e.g., electromagnetic
permittivity, magnetic permeability, etc.) of samples, it is to be
understood that the electromagnetic properties are merely
illustrative, and that other electromagnetic properties may be
determined as well, as will be understood by the person of ordinary
skill in the art.
[0043] Further, while the following description discussing
determining electromagnetic properties of particular samples (e.g.,
carbon nanotubes, graphene, etc.), it is to be understood that the
samples are merely illustrative, and that electromagnetic
properties of other samples may be determined as well, as will be
understood by the person of ordinary skill in the art.
[0044] Graphene is an allotrope of carbon whose structure is one
atom thick planar sheets of bonded carbon atoms densely packed in a
honeycomb crystal lattice. The crystalline or "flake" form of
graphite consists of many graphene sheets stacked together.
[0045] Carbon nanotubes (CNTs) are allotropes of carbon with a
cylindrical nanostructure which have unusual properties. Their name
is derived from their long hollow structure with walls formed by
one atom thick sheets of graphene. The sheets of graphene are
rolled at specific and discrete chiral angles to form the CNT, the
combination of the rolling angle and the radius of the tube
determines the properties of the CNT formed. CNTs are used in many
technical areas including, but not limited to, nanotechnology,
electronics, and optics.
[0046] As used herein, the term "electromagnetic signal" may be
understood to refer to an electromagnetic wave within the
measurement chamber. The term is also used to refer to the
electromagnetic waves that are received for processing.
[0047] Disclosed is a device for the measurement of electromagnetic
properties of small samples of synthesized materials using a
two-dimensional geometry. Because the disclosed device uses a
two-dimensional geometry, the device eases the alignment
requirements typical of devices using a three-dimensional
geometry.
[0048] The disclosed device comprises a measurement chamber and an
input/output port. The input/output port serves to transmit
electromagnetic signals into the measurement chamber. The
electromagnetic signals are reflected off of a sample inside the
measurement chamber to produce reflected electromagnetic signals.
The input/output port further serves to receive the reflected
electromagnetic signals from the measurement chamber. The
input/output port may include an antenna coupled to the measurement
chamber through which the electromagnetic signals are channeled for
both transmission and reception. Alternately, the input/output port
may include any of probes, waveguides, loops, antennas, apertures
or other suitable structures.
[0049] The electromagnetic signals transmitted by the input/output
port may be controlled through a controllable source of
electromagnetic energy. The controllable source may, for example,
allow for selection of a frequency of the electromagnetic signals.
The controllable source may be coupled to the input/output
port.
[0050] FIG. 1 is a schematic illustration of an example measurement
device 100, in accordance with an embodiment. As shown, the device
100 comprises a closed measurement chamber 110 that is shaped as an
irregular hexagon. The measurement chamber 110 is constructed as a
substantially two-dimensional chamber. To this end, the thickness
or depth of the measurement chamber 110 may be, for example, on the
order of the wavelength of the electromagnetic radiation used,
which may be in the range of, for example, millimeter or
sub-millimeter frequencies.
[0051] As shown, the measurement chamber 110 includes a reflective
surface 120 having an at least partly conic shape. In this
embodiment, the conic shape results from the substantially
elliptical reflective surface 120. Electromagnetic signals directed
into the measurement chamber 110 may reflect off the reflective
surface 120 onto a sample provided in the measurement chamber.
Further, electromagnetic signals directed out of the measurement
chamber 110 may reflect off the reflective surface 120 out of the
measurement chamber 110.
[0052] The substantially elliptical reflective surface 120 may form
part of an ellipse 130, as indicated by the dotted line. As shown,
the ellipse 130 is a regular ellipse having a first focal point 140
and a second focal point 150. An input/output port 160 may be
positioned at the first focal point 140. As shown, the input/output
port 160 includes an antenna 170 through which electromagnetic
signals may be coupled into and out of the measurement chamber 110.
Further, a sample holder (not shown) for holding the sample may be
positioned at the second focal point 150.
[0053] The electromagnetic signals coupled into the measurement
chamber 110 may be reflected off the reflective surface 120 towards
the sample. Further, the electromagnetic signals may be reflected
off the sample back towards the reflective surface 120, and may
reflect off the reflective surface 120 towards the input/output
port 160. At the input/output port 160, the electromagnetic signals
reflected off the sample may be coupled out of the measurement
chamber 110 using the antenna 170 and may be passed to a processor
(not shown) for processing. Based on the electromagnetic signals
reflected off the sample, the processor may determine the
permittivity and the permeability of the sample.
[0054] The processor may comprise a network analyser and a computer
that is connected to the input/output port 140 via a waveguide or a
coaxial cable. In some embodiments, the processor may also control
the generation of the electromagnetic signals that are coupled into
the measurement chamber 110.
[0055] In some embodiments, wall 180 of the measurement chamber 110
may be covered by electromagnetic absorbing material (not shown)
that prevents interference between electromagnetic signals
reflected from the walls of the measurement chamber 110 and the
electromagnetic signals reflected from the sample. In this way,
electromagnetic signals incident on the wall 180 of the measurement
chamber 110 are not reflected, but rather are absorbed so that only
the electromagnetic signals reflected from the sample in the sample
holder (not shown) are received at the input/output port 160 via
the antenna 170.
[0056] FIG. 2 is a schematic illustration of another example
measurement device 200, in accordance with an embodiment. As shown,
the measurement device 200 includes a measurement chamber 210. The
measurement chamber 210 may be a substantially two-dimensional
measurement chamber. Further, as shown, the measurement chamber 210
may comprise a first reflective surface 220 and a second reflective
surface 225. Each of the first and second reflective surfaces 220,
225 may be substantially elliptical. The first reflective surface
220 may form a part of a first ellipse 230, while the second
reflective surface 225 may form a part of a second ellipse 235. As
shown, the first ellipse 230 has a first focal point 240 and a
second focal point 250. Similarly, the second ellipse 235 has a
third focal point 245 and a fourth focal point 255. The second
focal point 250 and the fourth focal point 255 are coincident.
[0057] The measurement device 200 further includes a first
input/output port 260 and a second input/output port 265. The first
input/output port 260 includes an antenna 270 and is located at the
first focal point 240. The second input/output port 265 includes an
antenna 275 and is located at the third focal point 245. Each of
the first and second input/output ports 260, 265 may be connected
to a waveguide and/or a coaxial cable (not shown) at the outside of
the measurement device 200.
[0058] The measurement device further includes a sample holder,
which may be positioned at the coincident second and fourth focal
points 250, 255.
[0059] The measurement chamber 210 is defined by walls 280, 285 and
the elliptical surfaces 220, 225. In particular, as shown, the
walls 280, 285 form part of a housing 290 that is shaped to
accommodate the elliptical surfaces 220, 225. In some embodiments,
the walls 280, 285 may be covered with electromagnetic absorbing
material (not shown) to prevent electromagnetic signals reflected
from the walls 280, 285 from interfering with electromagnetic
signals reflected from and transmitted through the sample.
[0060] In operation, an electromagnetic signal is coupled into the
measurement chamber 210 by the antenna 270 at the first
input/output port 260. The electromagnetic signal is directed
towards the first reflective surface 220. The electromagnetic
signal is then reflected off of the first reflective surface 220
towards the sample in the sample holder at the coincident second
and fourth focal points 250, 255. Electromagnetic signals that pass
through the sample are reflected off of the second reflective
surface 225 towards the antenna 275 at the second input/output port
265. Similarly, electromagnetic signals that are reflected off of
the sample are in turn reflected off of the first reflective
surface 220 towards the antenna 270 at the first input/output port
260.
[0061] Each of the first and second input/output ports 260, 265 is
connected to a processor (not shown), such as a network analyzer
and a computer, by means of a waveguide and/or coaxial cable (not
shown). Based on the electromagnetic signals that passed through
the sample, and the electromagnetic signals reflected off the
sample, the processors may determine the permittivity and the
permeability of the sample. In some embodiments, the processors may
also control the generation of the electromagnetic signals that are
coupled into the measurement chamber 210.
[0062] In some embodiments, the electromagnetic signal may
alternatively be coupled into the measurement chamber 210 by the
antenna 275 at the second input/output port 270. In these
embodiments, the electromagnetic signal is directed towards the
second reflective surface 225. The electromagnetic signal is then
reflected off of the second reflective surface 220 towards the
sample in the sample holder at the coincident second and fourth
focal points 250, 255. Electromagnetic signals that pass through
the sample are reflected off of the first reflective surface 220
towards the antenna 270 at the first input/output port 260.
Similarly, electromagnetic signals that are reflected off of the
sample are in turn reflected off of the second reflective surface
225 towards the antenna 275 at the second input/output port
265.
[0063] Further, in some embodiments, electromagnetic signals may be
coupled into the measurement chamber 210 by both the antenna 270 at
the first input/output port 260 and the antenna 275 at the second
input/output port 270. For example, electromagnetic signals may be
coupled into the measurement chamber 210 by the antennas 270, 275
substantially simultaneously, or sequentially. In some embodiments,
the electromagnetic signals coupled into the measurement chamber
210 by the antennas 270, 275 may have different frequencies.
[0064] As noted above, the sample holder holding the sample may be
placed at the coincident second and fourth focal points 250, 255.
The coincident second and fourth focal points 250, 255 may act as
an energy source and radiate electromagnetic signals towards the
antennas 270, 275.
[0065] Scattering parameters (S-parameters) may be (e.g.,
continuously) measured at one or both of the first and second
input/output ports 260, 265. In some embodiments, insertion loss
and return loss may be measured. Insertion loss is an expression of
the magnitude of the transmission coefficient |S21| in dB and
return loss is an expression of the magnitude of the reflection
coefficient |S11| in dB. The insertion loss may, for example, be
measured to be less than 1 dB for the microwave V band (e.g.,
between 50 and 75 GHz). Similarly, the return loss may, for
example, be measured to be less than 10 dB for the microwave V
band.
[0066] FIG. 3 illustrates a radiation field distribution in the
example measurement device 200 shown in FIG. 2, in accordance with
an embodiment. As shown in FIG. 3, the antennas 270, 275 comprise
H-plane horn antennas that radiate electromagnetic signals towards
the first and second reflective surfaces 220, 225, respectively.
The horn antennas 270, 275 are implemented in a
semi-two-dimensional configuration in an x-y plane such that the
electromagnetic signals are confined in the z-direction, resulting
in a reduced loss due to diffraction. The electromagnetic signal
radiated by the first horn antenna 270 is reflected first off the
first reflective surface 220 and then off the second reflective
surface 225 before being received by the second horn antenna
275.
[0067] As shown, the horn antenna 270 is placed at the first focal
point 240 and the horn antenna 275 is placed at the third focal
point 245. As a result, the electromagnetic signals radiated by the
horn antennas 270, 275 are focused at the coincident second and
fourth focal points 250, 255. This focusing may allow the
measurement device 210 to have increased sensitivity to the
electromagnetic properties of the sample.
[0068] In the measurement device 210, the electromagnetic signals
may be confined by the first and second reflective surfaces 220,
225 and the walls 208, 285 of the housing 290. Minor leaking may
occur through a gap 310 between the first and second reflective
surfaces 220, 225 and around the ends 320, 325 of the first and
second reflective surfaces 220, 225 adjacent to the first and third
focal points 240, 245. In some embodiments, the walls 280, 285 may
be covered in electromagnetic absorbing material so that the walls
208, 285 do not reflect any electromagnetic signals in the
measurement chamber 210.
[0069] FIG. 4 is a perspective illustration of the example
measurement device shown in FIG. 2, in accordance with an
embodiment. As shown, the measurement device 400 includes a base
portion 410 and a top portion 420 that define a measurement chamber
430. The base portion may have dimensions on the order of, for
example, 10 centimeters by 20 centimeters, and may be formed of,
for example, aluminum, brass, or silicon with a metallised
interior. The height of the measurement chamber 430 may be on the
order of, for example, about 2 mm, thereby providing a
substantially two-dimensional arrangement at the microwave V band.
The top portion 420 may comprise a substantially planar metallic
cap sized to be the same as the dimensions of the base portion 410.
Other dimensions and other materials are possible as well.
[0070] The base portion 410 is shaped to provide a generally
semicircular recess that defines the measurement chamber 430. First
and second reflective surfaces 440, 445 are provided as shown
together with first and second input/output ports 450, 455. The
first and second reflective surfaces 440, 445 may be substantially
elliptical.
[0071] As in the above example measurement devices, the first and
second reflective surfaces 440, 445 may each form a part of
ellipses. The ellipses may have one coincident focal point and may
each have one non-coincident focal point. The first and second
input/output ports 450, 455 may be located at the non-coincident
focal points of the ellipses.
[0072] In the embodiment shown in FIG. 4, the first and second
input/output ports 450, 455 may be configured to connect to
standard waveguides such as, for example, the WR15 waveguide 460
shown, or any other waveguide suitable for use in the microwave V
band.
[0073] In order to avoid unwanted resonances from the edges of the
measurement chamber 430, absorbers 470, 480 may be placed along the
substantially semicircular recess that defines the measurement
chamber 430. The first and second input/output ports 450, 455 may
be left clear. Such absorbers may comprise, for example, carbon or
a graphite-based material.
[0074] As in the above example measurement devices, a sample holder
for holding a sample may be placed at the coincident focal point of
the ellipses. The coincident focal point may act as an energy
source to radiate electromagnetic signals towards the first and
second input/output ports 450, 455.
[0075] FIG. 5 is a schematic illustration of another example
measurement device 500, in accordance with an embodiment. As shown,
the measurement device 500 comprises a measurement chamber 510
comprising two ellipses (not shown). The first ellipse has a first
focal point 520 and a second focal point 525, while the second
ellipse has a third focal point 530 and a fourth focal point 535.
The second and fourth focal points 525, 535 are coincident, while
the first and third focal points 520, 530 are non-coincident.
[0076] A portion of each ellipse forms a substantially elliptical
reflective surface 540, 545 that reflects electromagnetic signals
onto a sample holder (not shown) placed at the coincident second
and fourth focal points 525, 535.
[0077] The measurement device 500 further comprises first and
second input/output ports 550, 555 arranged to be connected to a
waveguide or coaxial cable (not shown) at the outside of the
measurement chamber 510 and to two open-ended waveguides (not
shown) directed towards the measurement chamber 510. As shown, the
first input/output port 550 is placed at the first focal point 520,
and the second input/output port 555 is placed at the third focal
point 530. That is, the first and second input/output ports 550,
555 are placed at the non-coincident first and third focal points
520, 530.
[0078] In operation, a sample may be placed in the sample holder at
the coincident second and fourth focal points 525, 535, and the
first input/output port 550 and/or the second input/output port 555
may transmit an electromagnetic signal into the measurement chamber
510. The coincident second and fourth focal points 525, 535 may act
as an additional energy source and radiate electromagnetic signals
towards the first and second input/output ports 550, 555.
[0079] FIG. 6 illustrates a radiation field distribution in the
example measurement device shown in FIG. 5, in accordance with an
embodiment. As shown, the field distribution is bounded by the
measurement chamber 510. The electromagnetic signals transmitted by
the first and second input/output ports 550, 555 are shown to focus
at the coincident second and fourth focal points 525, 535.
[0080] FIG. 7 illustrates a graph 700 of insertion and return
losses as a function of frequency for an example measurement
device, in accordance with an embodiment. Return loss is indicated
by dotted profile 710 and insertion loss is indicated by solid line
720. As will be apparent to the person of ordinary skill in the
art, the insertion and return loss may be used to determine
electromagnetic properties of the sample. In this manner, return
loss may be optimized.
[0081] Although the present invention has been described with
reference to specific embodiments, it will be appreciated that
other configurations of measurement devices are possible provided
there is an overlapping focal point which can be determined from
the surface geometry of the elliptical surfaces.
* * * * *